In 1975, Kohler and Milstein established the technique for producing monoclonal antibodies, which provided a new method for treatment of tumors, the targeted therapy of tumors. In the preliminary study of the targeted tumor therapy, great enthusiasm and impractical expectation was held, but the therapeutic effects during the early clinical researches were undesired, mainly because: (1) murine antibodies were exploited in the early clinical researches, which could inducing human antibodies against murine antibodies (HAMA) that could neutralize the therapeutic murine antibodies so that the murine antibodies were quickly cleared off, had a relatively short half-life in human body, and thus their therapeutic effects were uncertain; Moreover, murine antibodies could stimulate allergic responses in human body, thereby may cause toxic negative effects; (2) the affinity and specificity of the antibodies were not high enough, and most antibodies, especially some genetic engineered small molecular antibodies or humanized antibodies had a relatively low affinity and specificity, and thus could not be effectively targeted to tumor cells, so the antitumor effect was not definite in clinic; and (3) success of antibody therapy further depends on the factors of the differences of tumor antigen expression per se and the modulations of antigens. During the recent 5 years, with the development of modem biological technology, two critical techniques with regard to antibody production were solved by scientists, that is: (1) the development of the technology of murine-human chimeric antibodies, humanized antibodies and human antibodies, as well as their production techniques substantially solving the problems associated with the generation of anti-antibodies when murine antibodies were applied to human; in the meantime, because of the use of human Fc fragment (crystallizable fragment, which represents the fragment obtained by digesting immunoglobulin with papain and having a molecular weight of about 50,000) in human-murine chimeric antibodies, humanized antibodies and human antibodies, the half life of the antibodies was extended to several days, even up to 21 days, which was obviously longer than the half life of murine antibodies (shorter than 20 hours); in addition, the modification of human Fc fragment could further improve the effect of killing tumor cells; and (2) with the development of techniques for constructing and screening antibody libraries and for preparing multivalent recombinant antibodies, monoclonal antibodies with high specificity and affinity could be directly obtained, for example, the affinity of an antibody produced by the Selected Lymphocyte Antibody Method (SLAM) is 1000 folds higher than that of an antibody produced by the hybridoma technique. With the development of antibody technologies, the progress of the targeted therapy is finally obtained; some breakthroughs were made during the recent years. The treatment of tumor with antibodies is a promising strategy for the first time.
However, there are still two difficulties in the treatment of solid tumors with antibodies: (1) solid tumor cells are surrounded by dense matrix, so antibodies can hardly penetrate through this barrier to reach tumor cells; obstruction of lymphatic reflux in most solid tumors results in the increase of interstitial pressure and thereby preventing the antibodies in blood from entering the tumor stroma; Even if a small portion of antibodies enters into tumors, they will firstly contact and bind to perivascular tumor cells, and thus cannot reach tumor cells distal to the blood stream; and (2) a great amount of antibody is needed for tumor treatment, which cannot be achieved by the present biological engineering techniques; Moreover, due to the required high quantity and quality of antibodies, the cost of antibody production is very expensive, so that such antibodies are very expensive. Accordingly, the therapeutic effects on large-volume solid tumors with antibodies are undesirable at present. It is suggested in many studies that the antibody therapy for solid tumors should mainly be directed to minor residues of tumor or micrometastasis focus. However, the therapeutic effects of such treatment can only be estimated by a long period study and by a large scale of multicenter clinical trials, which also limits the clinical application of antibodies for treatment of solid tumors.
Gene therapy is a novel method which was developed in recent years for treatment of malignant tumors. The gene transfection methods are classified into two types: viral or non-viral. The viral method usually uses retrovirus, recombinant adenovirus, adeno-associated virus, herpes simplex virus and Vaccinia virus. Retrovirus has relatively high transfection efficiency in vitro, but has relatively low virus titer and relatively low transfection efficiency in vivo; in addition, retrovirus can only infect dividing cells, and has a shortcoming of integrating into cell genomes to cause tumor genesis. Non-viral methods comprise liposome method, gene gun method, etc., but the transgene is expressed for a relatively short period, and the transfection efficiency is lower. Adenovirus and adeno-associated virus are the commonly used viral vectors for gene therapy of tumor at present, and are widely used in many human gene therapy. Adenovirus has advantages of easy production and purification. It can effectively transfect dividing cells and resting cells in vivo and in vitro. Moreover, it will not induce tumor genesis. Adeno-associated virus is capable of transfecting dividing cells and resting cells, and can be expressed permanently. The treatment of tumor with recombinant virus carrying single-chain antibody or Fab antibody has been reported (Alvarez R D, Barnes M N, Gomez-Navarro J, et al., A cancer gene therapy approach utilizing an anti-erbB-2 single-chain antibody-encoding adenovirus (AD21): a phase I trail. Clin. Cancer Res. 2000, 6:3081-7). However, due to the short half-life of the single-chain antibody or Fab antibody in vivo and the lack of antibody-mediated cytotoxicity, their therapeutic effects are undesirable. In contrast, full-length antibodies containing human constant regions, including human-murine chimeric antibodies, humanized antibodies and human antibodies, all have human light-chain constant regions and human heavy-chain constant regions, and thus will have a greatly extended half-life of several days, even up to 21 days. Moreover, said antibodies exhibit an obvious antibody-mediated cytotoxicity.
So far, the use of recombinant virus carrying a gene encoding tumor-therapeutic full-length antibody containing human constant regions is not reported.